Neutrophils are an essential element of host defense. The activation of neutrophils with chemotactic factors like the formylpeptides direct neutrophil movement from the intravascular space into tissues. This emigration requires both locomotion and shape change by neutrophils. These motile phenomena are likely linked to alterations in microfilamentous cytoskeleton which include changes in the content and distribution of F-actin. Neither the cellular responses associated with cytoskeletal change nor the molecular mechanisms which control cytoskeletal and motility in neutrophils are well characterized. Our long range goal is to understand 1) the relationship of locomotion and shape of neutrophils to changes in the cell's microfilamentous cytoskeletal organization and 2) the molecular mechanisms for control of cytoskeletal organization and motility of neutorphils. We will utilize fMLP to modify motility and cytskeletal organziation in neutrophils and quantify locomotive behavior, shape, F-actin content/distribution and actin-actin regulatory protein interactions by, respectively, single cell locomotion assays, photomicrography and computerized videoimage analysis, NBDphallacidin binding and immunoabsorption assays for gelsolin and profilin. Our specific aims are to: 1) Examine the roles of F- actin content/distribution and actin polymerization/depolymerization is determining shape and locomotion of neutrophils; 2) Describe the temporal/spatial relationship of gelsolin-actin interactions to change in F-actin content/distribution in neutrophils; 3) Examine the role of Ca++ and P1P2 in regulating gelsolin-actin interactions and nucleating activity in neutrophils; 4) Study the role of P1P2 in regulating profilinactin interactions and their effects on F-actin content on neutrophils. These studies have signficance for both and basic research. They will elucidate and describe cellular and molecular mechanisms involved in the control of motility and microfilamentous cytoskeletal organization of neutrophils, they will shed light on biochemical defects in disorders of neutrophil movement and they will assist in the development of agents which inhibit pathologic activation of motile response in diseases like adult respiratory distress syndrome and arthritis.